Research is being done on protein-nucleic acid interactions and on the structure and behavior of macromolecules in solution. Most of the work is concentrated on genetically well-characterized bacteriophage systems. Of particular interest are the virion of filamentous bacteriophage (fd) and the complex formed between fd DNA and a soluble DNA-binding protein which is involved in DNA replication and fd bacteriophage morphogenesis. Being sought is information on the chemical groups critically involved in DNA-protein binding, the conformational requirements of such binding, and cooperativity effects that are important in these systems. The effects of genetic mutation and solvent conditions on the conformation, stability and behavior in solution of nucleoprotein complexes are being investigated. In related work, the molecular weights, shapes, and thermodynamic interactions of flexible rod particles are being obtained by light scattering, sedimentation equilibrium and hydrodynamic methods.